This would depend on what the annual interest rate is. The formula that you would use to solve this equation with the information that is needed is:
Interest= Principle x interest rate x term (time)
In your case you would put the amount of interest first, then leave the principle amount as unknown. Once you know the interest rate you can fill that in next, along with the time, 12 months. Your equation would look something like this:
$30,000=p x ?(interest rate) x 12
Then you would times the principle amount times the term (length of time), divide both sides of the equation by your answer to solve for "P".
As starriegyrl1 points out, it will depend on your interest rate. The problem is that right now interest rates are incredibly low, even for "riskier" investments. Checking accounts have much lower interest rates than say savings accounts. And, savings accounts have lower interest rates than CDs.